This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cellulitis is a common infection of the skin and its underlying tissues. In 2004, $3.7 billion were spent on 240,000 adult hospitalizations for cellulitis in the United States. However, a University of Rochester pilot study showed that 20% of patients admitted to the hospital with a presumed diagnosis of cellulitis were diagnosed incorrectly. We hypothesize that a visual clinical decision support system &#40;VisualDx&#41;will assist physicians in diagnosing cellulitis, which will help avoid unnecessary hospitalizations, antibiotic administration, and healthcare spending. Historically, group A streptococci was the most common cause of cellulitis, with Staph aureus responsible for a minority of cases. Contrary to this view, Dr. Loren Miller &#40;co-investigator&#41;and colleagues&#39;review of the literature found that among patients with cellulitis who undergo needle aspiration cultures, the ratio of Staph aureus to group A streptococcal isolates is greater than three to one. Antibiotic resistance among Staph aureus emerged as soon as penicillin was introduced to treat staphylococcal infections in the 1940s, and it restricts and reshapes therapeutic options. Community outbreaks and dramatic increase of community-associated MRSA &#40;CA-MRSA&#41;disease have occurred in numerous populations including: prisoners, military personnel, athletes, daycare attendees, and families. CA-MRSA is endemic in Los Angeles County and typically causes infections in persons without contact with so-called &quot;at risk&quot;populations. The intersection of cellulitis and CA-MRSA is important. Given the most common known cause of cellulitis is Staph aureus, and the majority of Staph aureus infections from the community are caused by CA-MRSA, we hypothesize that empiric treatment of cellulitis may need to incorporate treatment for MRSA. The aims of this study are to determine the accuracy of diagnosis of patients with suspected cellulitis or erysipelas &#40;a similar superficial infection often caused by Streptococcus pyogenes&#41;, to identify risk factors associated with cellulitis infection, and to analyze the molecular epidemiology of CA-MRSA colonization among patients with cellulitis. We will enroll 160 patients admitted to Harbor-UCLA inpatient wards in a 1:2 paired case-control study. First, we will enroll 60 patients with suspected cellulitis. We anticipate 83% of 60 patients &#40;n&#61;50&#41;will have cellulitis. Cellulitis cases are defined as patients admitted to the inpatient wards with a dermatologist-confirmed diagnosis of uncomplicated cellulitis or erysipelas. There will be no gender or racial/ethnic-based enrollment restrictions. Controls, matched at a 1:2 ratio, are defined as uninfected subjects admitted to the inpatient wards who are matched to cellulitis cases by 3 criteria: age &#40;within 5 years&#41;, gender, and race/ethnicity. The study coordinator will identify patients admitted from the Emergency Department with a primary diagnosis of cellulitis or erysipelas. If the patient provides consent, the study coordinator will administer a questionnaire, photograph skin lesions, collect nasal and inguinal fold bacterial swab cultures, collect pertinent past medical history, and perform a directed physical exam. The study coordinator will also record laboratory data, collect data generated by inpatient resident physicians utilizing the computerized clinical decision support tool. Loss of privacy is the main risk, and while there are no direct benefits for the participant, participating may help future patients with cellulitis.